Optical measurements with dynamic range and high speed

ABSTRACT

A system for providing optical measurements and detection in optical spectrum analyzers (OSAs) with high dynamic range and high speed is disclosed. The system may include a slit to allow inward passage of an optical beam. The system may also include an optical portion to receive the optical beam. In some examples, the optical portion may include at least one optical splitter to split the optical beam into at least two optical paths. The system may also include an electrical portion to receive the optical beams split into the at least two optical paths. In some examples, the electrical portion may include at least one photodetector to receive each of the split optical beam. The electrical portion may also include at least one amplifier communicatively coupled to each of the at least one photodetector to amplify the split optical beam. The electrical portion may further include at least one analog-to-digital converter (ADC) communicatively coupled to each of the at least one amplifier to convert the split optical beams into digital signals.

TECHNICAL FIELD

This patent application is directed to optical measurementinstrumentation for telecommunication networks, and more specifically,to optical measurements and detection in optical spectrum analyzers(OSAs) with high dynamic range and high speed detection.

BACKGROUND

Optical measurement instrumentation, such as optical spectrometers oroptical spectrum analyzers (OSAs), play an important role in modernscientific research. Optical spectrum analyzers (OSAs), in particular,are vital in fiber-optics and optical communication technologies. Fromresearch and development (R&D) applications to manufacturing, opticalspectrum analyzers (OSAs) and other similar equipment have becomeessential to build and characterize a variety of fiber-optics products,such as broadband sources, optical sources, and wavelength divisionmultiplexed (WDM) systems.

BRIEF DESCRIPTION OF DRAWINGS

Features of the present disclosure are illustrated by way of example andnot limited in the following Figure(s), in which like numerals indicatelike elements, in which:

FIG. 1 illustrates a system for providing high resolution opticalmeasurements, according to an example;

FIG. 2 illustrates a diagram for fiber delivery to photodiodes in anoptical measurement system, according to an example;

FIGS. 3A-3B illustrate graphs of analog-to-digital converter (ADC)outputs, according to an example;

FIG. 4 illustrates a graph that stitches multiple analog-to-digitalconverter (ADC) outputs, according to an example;

FIGS. 5A-5B illustrate graphs of reconstructed optical spectrums,according to an example; and

FIG. 6 illustrates a flow chart of a method for providing opticalmeasurements using high dynamic range and high speed detection,according to an example.

DETAILED DESCRIPTION

For simplicity and illustrative purposes, the present disclosure isdescribed by referring mainly to examples and embodiments thereof. Inthe following description, numerous specific details are set forth inorder to provide a thorough understanding of the present disclosure. Itwill be readily apparent, however, that the present disclosure may bepracticed without limitation to these specific details. In otherinstances, some methods and structures readily understood by one ofordinary skill in the art have not been described in detail so as not tounnecessarily obscure the present disclosure. As used herein, the terms“a” and “an” are intended to denote at least one of a particularelement, the term “includes” means includes but not limited to, the term“including” means including but not limited to, and the term “based on”means based at least in part on.

There are many types of optical spectrum analyzers (OSAs), such asFabry-Perot-based, interferometer-based, and swept coherent heterodyneoptical spectrum analyzers (OSAs). However, one of the most commonoptical spectrum analyzers (OSAs) for fiber-optics applications includediffraction grating based optical spectrum analyzers (OSAs). These mayalso be commonly referred to as monochromator-based optical spectrumanalyzers (OSAs).

In a monochromator-based optical spectrum analyzer (OSA), for example, abroadband light from a bright and small light source may strike adiffraction grating. When this happens, a thin space between every twoadjacent lines of the diffraction grating may become an independent“source,” which may then diffract light off into a range of waveletangles. For each wavelength and each specific angle, the diffractedwavelets may be generated at exactly one wavelength out of phase withone another, and may therefore add together constructively. In otherwords, light with a given wavelength may leave the diffraction gratingat a specific angle. Also, the wider an illuminated portion of thediffraction grating, the higher the number of diffracted wavelets theremay be, and therefore the narrower the diffracted beam pattern maybecome. This may enable a spectral resolution of the monochromator-basedoptical spectrum analyzer (OSA) to be proportional to the size of theilluminated portion of the diffraction grating.

In general, an optical spectrum analyzer (OSA) may function by angularspreading an input spectrum using diffraction orders of a grating andusing a rotating reflector (e.g., a prism) to sweep through that inputspectrum. For any given angle of the rotating reflector, only a smallband of the input spectrum may be aligned with an output slit, which, inthis case, may be composed of an optical fiber that serves as an outputcoupler. In some examples, the output fiber may guide an output opticalbeam into a detection system (e.g., photodetector system), which may becomposed of various opto-electrical elements, such as photodiodes,amplifiers, and/or analog-to-digital converters (ADCs). The detectionsystem, among other things, may measure power as function of reflectorangle, which in turn may correspond to a function of wavelength.

A technical issue with conventional optical spectrum analyzers (OSAs)may include obtaining optical measurements and detection with highdynamic range and high speed detection. Although speed of rotation ofthe rotating reflector may help determine speed of the optical spectrumanalyzer (OSA) acquisition, it should be appreciated that the circuitryof the detection system itself may also affect a maximum sweep speed.For example, this may generally be due to amplifier response time orbandwidth. In other words, the detection system may be a contributingfactor that limits the maximum dynamic range of the power versuswavelength measurement in optical measurement systems using limited anamplifier with limited capabilities.

More specifically, a challenge with conventional optical spectrumanalyzers (OSAs) may include achieving a speed of greater than 1000nm/s. For example, to reach this goal, a detection system may also berequired to maintain a high dynamic range (e.g., >70 dB). Log amps maybe used in some scenarios, but these may prove to be particularly slowat low power levels. Linear amplifiers may be used as well, but theyhave proven to have low dynamic range. Switchable range linearamplifiers may be utilized, but they may be slow due to time needed toswitch gain stages. These and other drawbacks may be experienced whenconventional approaches are implemented, particularly with the types ofamplifiers as described.

The systems and methods described herein, however, may achieve highspeed optical measurements while maintaining high dynamic range withoutsacrificing compact designs of existing optical spectrum analyzers(OSAs). The systems and methods described herein may help reduce oreliminate all the drawbacks of the linear amplifiers. In some examples,this may be achieved by constructing a multistage parallel systemwithout a need to switch gain ranges. In this example, all or most gainranges may be captured simultaneously and the analog signals have beenconverted to digital signals with 16 bit quantization may then bestitched together.

In this way, the systems and methods described herein may cover thedesired dynamic range with multiple gain stages. Using thisconfiguration, the amplifier bandwidth may be independent on the inputpower which may allow for minimal distortion of the optical signal atall power levels. Digital signal processing may also be used to furtherimprove the fidelity of the acquired spectrum. These and other benefitsand advantages may be apparent in the examples outlined below.

FIG. 1 illustrates a system for providing high resolution opticalmeasurements, according to an example. In some examples, the system 100may depict a multi-pass optical spectrum analyzer (OSA). As shown, thesystem 100 may be a four-pass (4-pass or quad-pass) monochromator-basedoptical spectrum analyzer (OSA). The system 100 may include an input orentrance slit 102, an optical beam 104, a grating element 106, aretroreflective element 108, a mirror element 110, and an output or exitslit 112.

It should be appreciated that one or more additional optical elementsmay also be provided. For example, a light source (not shown) may beprovided upstream of the input or entrance slit 102 to generate abroadband beam, light, or optical signal. A detection system (not shown)may also be provided downstream of the output or exit slit 11 to collectand measure the optical beam 104. Other optical elements may also beprovided. For instance, one or more collimators or lenses may beprovided between the input slit 102/output or exit slit 112 and thegrating element 106 to collimate or focus the optical beam 104 asneeded. For simplicity, the components and elements shown in system 100may helpful to illustrate the multi-pass configuration and design toachieve a high resolution optical measurements.

The input or entrance slit 102 and output or exit slit 112 may enable orallow the optical beam 104 to pass through. In some examples, the inputor entrance slit 102 and output or exit slit 112 may positioned by 1millimeter (mm) or less apart. Other distances, dimensions, orvariations may also be provided to obtain the desired opticalmeasurement.

In some examples, the grating element 106 may be a diffraction grating.As such, the diffraction grating may be an optical component with aperiodic structure that splits or diffracts light into separate beamsthat may also travel in different directions. In some examples, thediffraction grating may be a ruled, holographic, or other similardiffraction grating. The grating element 106 may also be configured,among other things, with various properties that include transparency(transmission amplitude diffraction grating), reflectance (reflectionamplitude diffraction grating), refractive index or optical path length(phase diffraction grating), and/or direction of optical axis (opticalaxis diffraction grating). The grating element 106 may also be made froma variety of materials. This may include any number of isotropicmaterials. In some examples, the grating element 106 to be used insystem 100 may be selected based on any number of factors to optimizethe resolution of the optical spectrum analyzer (OSA). This may includefactors, such as efficiency, blaze wavelength, wavelength range, straylight, resolving power, etc.

The retroreflective element 108 may include any number ofretroreflective element configurations to provide retroreflection orother similar function. For example, the retroreflective element 108 maybe a prism reflector, a flat mirror, or a mirror and lens combination.In some examples, the mirror may be a convex mirror and the lens may bea focusing lens. It should be appreciated that other retroreflectiveelements, configurations, or combinations of such elements orconfigurations, may also be provided.

Referring back to system 100 of FIG. 1, the mirror element 110 may be aflat mirror or other reflective element. These may include, but notlimited to, any number of reflective materials, such as quartz, glass,metal (e.g., aluminum, etc.), silicon, or other materials withhigh-reflection (HR) coatings (e.g., dielectric, magnesium, fluoride,etc.).

As shown in system 100 of FIG. 1, the optical beam 104 may travel fromoptical element to optical element. In this case, the optical beam 104may pass through the same grating element 106 four times between theinput or entrance slit 102 and the output or exit slit 112, themulti-pass monochromator-based optical spectrum analyzer (OSA) of system100 may be referred to as a four-pass (4-pass or quad-pass)monochromator-based optical spectrum analyzer (OSA) that is able, bydesign, to achieve high resolution optical measurements.

FIG. 2 illustrates a block diagram 200 for fiber delivery to photodiodesin an optical measurement system, according to an example. As describedabove, an optical spectrum analyzer (OSA), such as the system 100 ofFIG. 1, may function by angular spreading an input spectrum usingdiffraction orders of a grating element and using a rotating reflector(e.g., a prism) to sweep through that input spectrum. For any givenangle of the rotating reflector, only a small band of the input spectrummay be aligned with the output or exit slit 112, which, in this case,may be composed of an optical fiber 201, as shown in the block diagram200 of FIG. 2. In some examples, the optical fiber 201 may also serve asan output coupler. Furthermore, the optical fiber 201 may guide anoutput optical beam into a detection system (e.g., photodetector system)having an optical portion 210 and an electrical portion 220, both ofwhich may be composed of any number of photodiodes, amplifiers,analog-to-digital converters (ADCs), and/or other opto-electricalelements. The detection system, among other things, may measure power asfunction of reflector angle, which in turn may correspond to a functionof wavelength.

As shown, the optical portion 210 of the detection system may includeone or more splitters 212, such as splitters 212A and 212B. In someexamples, these splitters 212A and 212B may be asymmetric splitters(e.g., 90:10 splitters), which that direct the optical beam 104 invarious directions and proportions. A 90:10 splitter, for instance, maydirect 90% of the optical beam in one direction and 10% of the beam inanother. Although two 90:10 splitters are shown, splitting light inthree paths, it should be appreciated that other types (e.g.,symmetric), numbers, and/or additional (or less) splitters may be usedto direct light or the optical beam in any number of paths, directions,or proportions.

The electrical portion 220 of the detection system may include one ormore photodetectors (PDs) 222, such as PD1, PD2, and PD3. Each of thePDs 222 shown in FIG. 2 may be connected to amplifiers 224, such asAMP1, AMP2, AMP3, and AMP4. In some examples, these amplifiers 224 maybe linear amplifiers, or other types of amplifiers, with varyingspecifications that may provide for suitable (or various) gain ranges tocover any desired dynamic range. It should be appreciated that gainstages, in some examples, may be designed to have approximately a samebandwidth as was chosen to match a desired optical spectrum analyzer(OSA) resolution.

The block diagram 200 of FIG. 2 may illustrate how an optical beam 104traverses an optical measurement system 100, as shown in FIG. 1, andthrough the output or exit slit 112, which may be an optical fiber 201.Once the light passes through the optical fiber 201, the light oroptical signal in the optical fiber 201 may be divided by at least twosplitters 212A and 212B, as shown in an optical portion 210. In someexamples, these at least two splitters 212A and 212B may be asymmetricsplitters that direct the light or optical signal into three paths in90:10 proportions. These three paths may eventually carry light into anelectrical portion 220. For example, these three paths may lead to atleast three photodetectors, such as PD1, PD2, and PD3. Eachphotodetector 222, which may be a photodiode or other similarphotodetector, may be communicatively coupled to an amplificationcircuit (or multiple stages of amplification), which may include anynumber of amplifiers 224. As shown, there may be at least four (4)amplifiers 224, such as AMP1, AMP2, AMP3, and AMP4, which may direct thesignal eventually to one or more analog-to-digital converters (ADCs)226, such as ADC1, ADC2, ADC3, and ADC4.

Each of the optical fiber paths may carry a specified ratio of light insuch a way that the lowest gain detection stage (e.g., PD1, AMP1, ADC1)may receive the lowest amount of light and the highest gain stage (e.g.,PD3, AMP3/AMP4, ADC3/ADC4) receive the largest ratio of optical light.Although at least two splitters 212A and 212B may be asymmetricsplitters that direct the light or optical signal into three paths in90:10 proportions, as shown, it should be appreciated that any otherratio may be used to maximize the dynamic range while maintaining someoverlap between each amplifier's range. This overlap may be necessaryfor stitching to be accomplished without gaps. For this optimization,wavelength dependent responsivity of the PDs may need to be considered,as well as bandwidth of amplifiers, and wavelength dependent couplingratios and optical insertion loss of the splitters. The 90/10 ratio,therefore, may simply be one of any number of exemplary proportions orratios.

Although the block diagram 200 of FIG. 2 is directed to delivery of datavia optical fibers, it should be appreciated that such data delivery mayinclude other variations as well that go beyond use of fiber-pigtailedphotodetector(s) in optical spectrum analyzers (OSAs). For example, thismay include any number of “free-space coupled” splitter variants foropen-air stitched-PD schemes. In fact, instead of fibers or fiber-basedsplitters, it should be appreciated that other circuitry with “bulk”optical elements, such using mirrors, prism based splitters, lenses tofocus light into PD, etc., may also be used to propagate the light ordata signals. Accordingly, the block diagram 200 is illustrative and notlimited only to optical fiber delivery.

FIGS. 3A-3B illustrate graphs 300A and 300B of analog-to-digitalconverter (ADC) outputs, according to an example. As shown, the graph300A may illustrate ADC output from the four analog-to-digitalconverters (ADCs) 226, and the graph 300B may illustrate ADC output inlogarithmic scale (“log scale”) from the four analog-to-digitalconverters (ADCs) 226. Both graphs 300A and 300B may also illustrateoutputs with a Gaussian optical input of 100 picometers (pm) bandwidth.This logarithmic representation may highlight sensitivity of each ADCoutput at power levels closer to a lower limit for each detector path.It may also show quantization effects that happen at this lower limit.This can be seen for example with the ADC1 (blue/dashed line) data: whenthe power reaches a level closer to the bottom limit of ADC1, steps canbe clearly seen in this log scale because ADC1 is operating at a powerlevel close to its lower limit. From this example, the advantages ofthis stitching approach may become clearer since the system may thenchoose to use information from ADC2 (orange/dashed line), instead ofADC1. This may also exemplify a need to choose splitting ratios and ADCranges carefully, in order to provide some overlap between a lower limitof one ADC and an upper limit of the next. As described in more detailherein, ADC outputs shown in graphs 300A and 300B of FIG. 3 may be usedor processed. In some examples, these ADC outputs may be used to recoverthe optical power information. For example, this may be achieved byusing one or more electrical constants of the optical components used ineach of the detection stages.

It should be appreciated that the optical power that passes through thedetection system in FIG. 2 may be converted to an ADC value by a chainof physical processes. For example, light arriving at the entrance ofthe detection system may be denoted as power P, for example, in theoptical fiber 201, as it passes through at least one optical splitter212A. In this scenario, there may be a certain amount of intrinsicinsertion loss and a transmission ratio to each port. The compoundeffects of all possible splitters and losses, in a given path, may thenbe represented by an effective transmittance T for that path. Lightpower P arriving at each photodiode may then be converted into anelectrical current by the responsivity R of the photodiode. Thiselectrical current may then be converted into electrical voltage by theamplifier with gain G. The voltage may then be measured or calculated byeach ADC by being converted into a digital number A, where A may bebetween 0 and the maximum quantization of the ADC (e.g., 2¹⁴−1, in thisexample, 14-bit quantization). The ADCs may have a maximum voltage thatis represented by the saturation voltage Vs. Thus, the entire conversionmay be summarized by the following equation:

$A = {\frac{P \cdot R \cdot T \cdot G}{V_{S}}{\left( {2^{14} - 1} \right).}}$

Here, the ADC values may be converted back to optical power by theinverse equation:

$P = {\frac{A \cdot V_{S}}{R \cdot T \cdot G \cdot \left( {2^{14} - 1} \right)}.}$

In this example, a dark current of the PDs may be ignored for simplicityof calculation. However, a real implementation may need to be calibratedafter being assembled, to determine an exact conversion between inputpower and ADC values. It should be appreciated that the constants shownin the equation may be simplified to a single constant that produces theconversion (measured during calibration). The equations shown above mayalso be wavelength dependent because some, but perhaps not all, of thesystem components may be dependent on the wavelength. Again forsimplicity, a wavelength dependent calibration may therefore be atrivial extension. It should be appreciated that each converted powerspectrum (e.g., one for each of the amplification paths of FIG. 2) mayhave a saturation level and a minimum power level. As a result, thisinformation may need to be further processed. For example, eachconverted power spectrum may be “stitched” together, as described below.

FIG. 4 illustrates a graph 400 that stitches multiple analog-to-digitalconverter (ADC) outputs, according to an example. As shown in graph 400,the four ADC outputs after converting the measurements from digitalvalues to optical power using the constant of the system, for example,may be combined or “stitched” together using a stitching technique orother similar approach. The stitching technique, for example, may bebased on one or more mathematical, image-based, or data-basedalgorithmic sequence. Other various examples or approaches may also beprovided.

In some examples, each of the spectra recovered from each of the ADCs,for example, may be stitched or combined to recreate a signal that mayrepresent the “original” signal with a dynamic range that is larger thanwhat would be possible using a single photodiode and amplifier circuit.In some examples, the stitching technique may select values, at eachwavelength point, from the highest gain stage that is not above apredetermined saturation level. Referring to the example shown in graph400 of FIG. 4, when starting from the left side of the spectrum, thepower value may be approximately −70 dBm and no ADCs may be insaturation. The values may be selected from ADC4 (highest gain stage)until approximately 1549.75 nm when ADC4 reaches a saturation point andvalues may start being selected from ADC3. At approximately 1549.8 nm,ADC3 may have reached its own saturation point and values from ADC2 mayhave become the relevant values for the final reconstructed spectrum.Finally, at approximately 1549.85 nm, ADC2 may have reached saturationand ADC1 (the lowest gain stage) may then become the selected path.

In some examples, a symmetric description may occur for wavelengthshigher than 1550 nm where power values decrease as a function ofwavelength and a choice of ADC path moves from ADC1 to ADC2 to ADC3 toADC4. It should be appreciated that the phrase, “symmetric description,”may be used herein to explain how the stitching starting from the leftto the middle may then be reversed from the middle to the right. Forexample, from left to right: ADC4→ADC3→ADC2→ADC1→ADC2→ADC3→ADC4. Thismay be true because the example shown may have a Gaussian profile. Asshown, the outputs for each of the ADCs 226 shown in FIG. 3 may be usedto recreate an “original” signal with a dynamic range that is largerthan and not possible using a single photodiode and amplifier circuit,as utilized in some conventional OSAs or related systems. Once theseoutputs are stitched together, a final optical spectrum may be provided.

FIGS. 5A-5B illustrate graphs 500A and 500B of reconstructed opticalspectrums relative to original input signal, according to an example.Both graph 500A and graph 500B may depict a reconstructed opticalspectrum compared to the original input signal. In other words, graph500A and graph 500B may be two representations of the same data set. Asshown, the input (blue/solid line) may be compared with the output(orange/dashed line). The input may be the original signal used tosimulate the system, and the output may be the resulting power spectrumafter simulating the detection circuit and applying the conversionequations. Thus, the only difference between graph 500A and graph 500Bis that the y-axis of graph 500A may show power in dBm units (log scale)and the y-axis of graph 500B may show power in mW units (linear scale).

It should be appreciated that additional signal processing of theoptical spectrum may further be provided by the stitching technique orother post-stitching action. For example, distortions created by limitedbandwidth of the amplification stages may be removed. Signal postprocessing may also become significant for measurements of narrowspectrum signals with higher or highest speeds. In other words, theadditional signal processing, by use of various techniques and/oralgorithms, may apply the equations described above to providestitching. The post processing techniques or algorithms may then beapplied to help eliminate or reduce distortions. In some examples, thismay involve a deconvolution action or a frequency “de-filtering.”Ultimately, such processing may optimize visualization and/or outputquality.

FIG. 6 illustrates a flow chart of a method for providing opticalmeasurements using high dynamic range and high speed detection,according to an example. The method 600 is provided by way of example,as there may be a variety of ways to carry out the method describedherein. Although the method 600 is primarily described as beingperformed by the system 100 of FIG. 1 and/or the system 200 of FIG. 2,the method 600 may be executed or otherwise performed by one or moreprocessing components of another system or a combination of systems.Each block shown in FIG. 6 may further represent one or more processes,methods, or subroutines, and one or more of the blocks may includemachine readable instructions stored on a non-transitory computerreadable medium and executed by a processor or other type of processingcircuit to perform one or more operations described herein.

At block 501, an optical signal may be received. In some examples, theoptical signal may be received from an optical beam. The optical beammay original from an optical fiber 201, or other optical communicationmedium.

At block 502, the optical beam may be split into at least two opticalpaths. In some examples, this may be achieved by using at least oneoptical splitter, such as an asymmetrical splitter, as described above.

At block 503, the split optical beam may be detected by at least onephotodetector, e.g., PD1, PD2, etc., as described above.

At block 504, the split optical beam may be amplified. In some examples,the split optical beam may be amplified using at least one amplifier,e.g., AMP1, AMP2, etc., as described above.

At block 505, the split optical beams may be converted into digitalsignals. In some examples, this may be achieved by using at least oneanalog-to-digital converter (ADC), e.g., ADC1, ADC2, etc., as describedabove.

As mentioned above, there may be numerous ways to configure or positionthe various optical elements of the system 100 or system 200, such asthe grating element 106, the retroreflective element 108, and/or themirror 110. Adjusting these and other components may also provide more amore efficient or compact design for the optical path of the opticalbeam 104. In this way, other electrical, thermal, mechanical and/ordesign advantages may also be obtained.

While examples described herein are directed to configurations as shown,it should be appreciated that any of the components described ormentioned herein may be altered, changed, replaced, or modified, insize, shape, and numbers, or material, depending on application or usecase, and adjusted for desired resolution or optimal measurementresults.

It should be appreciated that the systems and methods described hereinmay facilitate more reliable and accurate optical measurements. Itshould also be appreciated that the systems and methods, as describedherein, may also include or communicate with other components not shown.For example, these may include external processors, counters, analyzers,computing devices, and other measuring devices or systems. This may alsoinclude middleware (not shown) as well. The middleware may includesoftware hosted by one or more servers or devices. Furthermore, itshould be appreciated that some of the middleware or servers may or maynot be needed to achieve functionality. Other types of servers,middleware, systems, platforms, and applications not shown may also beprovided at the back-end to facilitate the features and functionalitiesof the testing and measurement system.

Moreover, single components may be provided as multiple components, andvice versa, to perform the functions and features described herein. Itshould be appreciated that the components of the system described hereinmay operate in partial or full capacity, or it may be removed entirely.It should also be appreciated that analytics and processing techniquesdescribed herein with respect to the optical measurements, for example,may also be performed partially or in full by other various componentsof the overall system.

It should be appreciated that data stores may also be provided to theapparatuses, systems, and methods described herein, and may includevolatile and/or nonvolatile data storage that may store data andsoftware or firmware including machine-readable instructions. Thesoftware or firmware may include subroutines or applications thatperform the functions of the measurement system and/or run one or moreapplication that utilize data from the measurement or othercommunicatively coupled system.

The various components, circuits, elements, components, and interfaces,may be any number of mechanical, electrical, hardware, network, orsoftware components, circuits, elements, and interfaces that serves tofacilitate communication, exchange, and analysis data between any numberof or combination of equipment, protocol layers, or applications. Forexample, the components described herein may each include a network orcommunication interface to communicate with other servers, devices,components or network elements via a network or other communicationprotocol.

Although examples are directed to test and measurement systems, such asoptical spectrum analyzers (OSAs), it should be appreciated that thesystems and methods described herein may also be used in other varioussystems and other implementations. For example, these may include anultra-narrow band tunable filter, an extended cavity diode laser, and/orapplied stages to further increase the spectral resolution of varioustest and measurement systems. In fact, there may be numerousapplications in optical communication networks and fiber sensor systemsthat could employ the systems and methods as well. The detection schemedescribed herein may have benefits in creating a large dynamic rangewithout compromising speed, which may be a desirable feature in opticalpower monitors or other similar systems.

It should be appreciated that the systems and methods described hereinmay also be used to help provide, directly or indirectly, measurementsfor distance, angle, rotation, speed, position, wavelength,transmissivity, and/or other related optical measurements. For example,the systems and methods described herein may allow for a higherresolution (e.g., picometer-level) optical resolution using an efficientand cost-effective design concept. By overcoming drawbacks of singlelinear amplifiers, a larger dynamic range with multiple gain stages maybe covered using the systems and methods described herein. With thisconfiguration, amplifier bandwidth may be independent on input power,which may allow for minimal distortion of optical signals at most or allpower levels. Furthermore, signal processing may be used to furtherimprove the integrity and fidelity of any acquired spectrum using thetechniques described herein.

With additional advantages that include high resolution, low number ofoptical elements, efficient processing techniques, cost-effectiveconfigurations, and small form factor, the systems and methods describedherein may be beneficial in many original equipment manufacturer (OEM)applications, where they may be readily integrated into various andexisting network equipment, fiber sensor systems, test and measurementinstruments, or other systems and methods. The systems and methodsdescribed herein may provide mechanical simplicity and adaptability tosmall or large optical measurement devices. Ultimately, the systems andmethods described herein may increase resolution, minimize adverseeffects of traditional systems (e.g., using single linear amplifiers),and improve measurement and processing efficiencies.

What has been described and illustrated herein are examples of thedisclosure along with some variations. The terms, descriptions, andfigures used herein are set forth by way of illustration only and arenot meant as limitations. Many variations are possible within the scopeof the disclosure, which is intended to be defined by the followingclaims—and their equivalents—in which all terms are meant in theirbroadest reasonable sense unless otherwise indicated.

1-20. (canceled)
 21. A system, comprising: at least one optical splitterto split an optical beam into at least two optical paths; at least onephotodetector to receive each of the split optical beam; at least oneamplifier communicatively coupled to each of the at least onephotodetector to amplify the split optical beam; at least oneanalog-to-digital converter (ADC) communicatively coupled to each of theat least one amplifier to convert the split optical beams into digitalsignals; and a processor to combine the digital signals using astitching technique.
 22. The system of claim 21, wherein the processorcomprises: generating an optical spectrum based on the combined digitalsignals, the optical spectrum representing an input optical signal. 23.The system of claim 22, wherein the stitching technique comprises:selecting values, at each wavelength point, from a highest gain stage ofthe digital signals that is not above a predetermined saturation level.24. The system of claim 21, wherein the optical splitter is anasymmetrical optical splitter.
 25. The system of claim 21, wherein thephotodetector is a photodiode.
 26. The system of claim 21, wherein theamplifier is a linear amplifier.
 27. The system of claim 21, wherein thesystem is a photodetection system for a multi-pass optical spectrumanalyzer (OSA).
 28. A method for providing optical measurement anddetection with high dynamic range and high speed, comprising: splitting,by at least one optical splitter of a detection system, the optical beaminto at least two optical paths; receiving, by at least onephotodetector of the detection system, the split optical beam; amplify,by at least one amplifier communicatively coupled to each of the atleast one photodetector, the split optical beam; convert, by at leastone analog-to-digital converter (ADC) communicatively coupled to each ofthe at least one amplifier, the split optical beams into digitalsignals; and combining, by a processor of the detection system, thedigital signals from the at least one analog-to-digital converter (ADC)by using a stitching technique.
 29. The method of claim 28, furthercomprising: generating, by the processor, an optical spectrum based onthe combined digital signals, the optical spectrum representing an inputoptical signal.
 30. The method of claim 29, wherein the stitchingtechnique comprises: selecting values, at each wavelength point, from ahighest gain stage of the digital signals that is not above apredetermined saturation level.
 31. The method of claim 28, wherein theoptical splitter is an asymmetrical optical splitter.
 32. The method ofclaim 28, wherein the photodetector is a photodiode.
 33. The method ofclaim 28, wherein the amplifier is a linear amplifier.
 34. The method ofclaim 28, wherein the detection system is a photodetection system for amulti-pass optical spectrum analyzer (OSA).
 35. A non-transitorycomputer-readable storage medium having an executable stored thereon,which when executed instructs a processor to perform a method asfollows: splitting the optical beam into at least two optical paths;receiving the split optical beam; amplify the split optical beam;convert the split optical beams into digital signals; and combining thedigital signals using a stitching technique.
 36. The non-transitorycomputer-readable storage medium of claim 35, further comprising:generating an optical spectrum based on the combined digital signals,the optical spectrum representing an input optical signal.
 37. Thenon-transitory computer-readable storage medium of claim 36, wherein thestitching technique comprises: selecting values, at each wavelengthpoint, from a highest gain stage of the digital signals that is notabove a predetermined saturation level.
 38. The non-transitorycomputer-readable storage medium of claim 35, wherein the stitchingtechnique is based on at least one mathematical sequence, image-basedsequence, or data-based algorithmic sequence.
 39. The non-transitorycomputer-readable storage medium of claim 35, further comprising:performing at least one post-stitching processing action to mitigatedistortions or aberrations.
 40. The non-transitory computer-readablestorage medium of claim 39, wherein the at least one post-stitchingprocessing action comprises a deconvolution action or a frequencyde-filtering.